U.S. patent application number 16/070039 was filed with the patent office on 2019-01-24 for method for depositing a cdte layer on a substrate.
This patent application is currently assigned to Fraunhofer-Gesellschaft zur Forderung der angewandten Forschung e.V.. The applicant listed for this patent is CTF SOLAR GmbH, Fraunhofer-Gesellschaft zur Forderung der angewandten Forschung e.V.. Invention is credited to Ludwig Decker, Christian Drost, Daniel Hirsch, Christian Kraft, Christoph Metzner, Henry Morgner, Bastian Siepchen, Bettina Spath, Krishnakumar Velappan, Torsten Werner, Olaf Zywitzki.
Application Number | 20190027634 16/070039 |
Document ID | / |
Family ID | 57984933 |
Filed Date | 2019-01-24 |
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United States Patent
Application |
20190027634 |
Kind Code |
A1 |
Morgner; Henry ; et
al. |
January 24, 2019 |
METHOD FOR DEPOSITING A CDTE LAYER ON A SUBSTRATE
Abstract
A method for depositing a CdTe layer on a substrate in a vacuum
chamber by means of physical gas phase deposition is provided. The
substrate is heated to a coating temperature before the deposition
process and then guided past a vessel in which CdTe is converted
into a vapour state, a gaseous component with an increased pressure
(compared to the vacuum in the vacuum chamber) flowing through at
least one inlet, against the substrate surface to be coated, such
that the gaseous component is adsorbed on the substrate surface to
be coated before the substrate is guided past the at least one
vessel.
Inventors: |
Morgner; Henry; (Dresden,
DE) ; Metzner; Christoph; (Dresden, DE) ;
Hirsch; Daniel; (Dresden, DE) ; Zywitzki; Olaf;
(Dresden, DE) ; Decker; Ludwig; (Dresden, DE)
; Werner; Torsten; (Dresden, DE) ; Siepchen;
Bastian; (Dresden, DE) ; Spath; Bettina;
(Dresden, DE) ; Velappan; Krishnakumar; (Dresden,
DE) ; Kraft; Christian; (Dresden, DE) ; Drost;
Christian; (Dresden, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fraunhofer-Gesellschaft zur Forderung der angewandten Forschung
e.V.
CTF SOLAR GmbH |
Munich
Dresden |
|
DE
DE |
|
|
Assignee: |
Fraunhofer-Gesellschaft zur
Forderung der angewandten Forschung e.V.
Munich
DE
CTF SOLAR GmbH
Dresden
DE
|
Family ID: |
57984933 |
Appl. No.: |
16/070039 |
Filed: |
February 3, 2017 |
PCT Filed: |
February 3, 2017 |
PCT NO: |
PCT/EP2017/052323 |
371 Date: |
July 13, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 14/0021 20130101;
C23C 14/02 20130101; C23C 16/306 20130101; H01L 31/1828 20130101;
H01L 31/0445 20141201; C23C 14/0629 20130101; H01L 31/0296
20130101; H01L 27/14696 20130101; C23C 14/562 20130101 |
International
Class: |
H01L 31/18 20060101
H01L031/18; C23C 14/06 20060101 C23C014/06; C23C 14/02 20060101
C23C014/02; C23C 14/56 20060101 C23C014/56; H01L 31/0296 20060101
H01L031/0296; H01L 31/0445 20060101 H01L031/0445; H01L 27/146
20060101 H01L027/146 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 3, 2016 |
DE |
10 2016 101 856.2 |
Claims
1. A method of depositing a CdTe layer on a substrate within a
vacuum chamber by means of physical gas phase deposition, the
method comprising: heating the substrate, prior to the deposition
process, to a coating temperature; guiding the substrate past at
least one vessel in which CdTe is converted to a vaporous state,
wherein a gaseous component having an elevated pressure relative to
the vacuum in the vacuum chamber flows through at least one inlet
against a surface of the substrate to be coated, wherein the
gaseous component is adsorbed at the surface of the substrate to be
coated before the substrate is guided past the at least one
vessel.
2. The method of claim 1, wherein the gaseous component comprises
at least one of the elements from the group of oxygen, nitrogen,
sulfur, chlorine, fluorine, phosphorus, arsenic, antimony, bismuth,
and tellurium.
3. The method of claim 1, wherein multiple vessels in which CdTe is
sublimed are arranged in succession in a direction of movement of
the substrate, and upstream of each of the vessels, the gaseous
component having the elevated pressure relative to the vacuum in
the vacuum chamber flows through at least one inlet against the
surface of the substrate to be coated.
4. The method of claim 1, wherein the substrate is guided
repeatedly past the at least one vessel.
5. The method of claim 1, wherein the gaseous component is
activated by means of a plasma.
6. The method of claim 1, wherein the CdTe layer is deposited by
means of CSS.
7. The method of claim 1, wherein the CdTe layer is deposited by
means of VTD.
8. The method of claim 1, wherein the CdTe vapor is activated by
means of a plasma.
Description
[0001] This application is a 371 nationalization of international
patent application PCT/EP2017/052323 filed Feb. 3, 2017, which
claims priority under 35 USC .sctn. 119 to German patent
application DE 10 2016 101 856.2, filed Feb. 3, 2016. The entire
contents of each of the above-identified applications are hereby
incorporated by reference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] The embodiments may be better understood with reference to
the following drawings and description. FIG. 1 shows a schematic
diagram of a device by means of which the method of the invention
is performable.
DETAILED DESCRIPTION
[0003] The invention relates to a method of depositing a CdTe layer
on a substrate, with which at least one additional chemical element
can be intercalated into the deposited layer.
[0004] CdTe layers are gaining increasing significance in the
semiconductor industry, primarily in the production of thin-film
solar cells or image sensors for cameras.
[0005] For the deposition of CdTe layers the process methodology of
"close space sublimation" with the abbreviation CSS is in
widespread use. In this methodology, granular CdTe is heated in a
vessel, which sublimes in the vessel and hence is converted to a
vaporous state. A substrate which is to be coated and heated to
coating temperature is moved over the vessel, usually at close
quarters, as a result of which CdTe is deposited on the substrate
surface.
[0006] The deposition of CdTe layers by means of CSS for thin-film
solar cells is described, for example, in"CdTe
DUnnschichtsolarmodule auf dem Weg zur Produktion" [CdTe Thin-Film
Solar Cell Modules on the Way to Production], Dr. Dieter Bonnet,
FVS Themen 2000, pages 116-118.
[0007] DE 10 2014 202 961 A1 discloses a method of producing a
p-doped CdTe layer in which two CdTe sublayers are deposited, for
example by means of CSS, and a sacrificial layer comprising the
doping element between the two sublayers. The doping element
diffuses from the sacrificial layer into adjoining regions of the
CdTe sublayers.
[0008] Alternatively, it is also possible to conduct a reactive
deposition operation in the CSS process by admitting a reactive
gas, for example oxygen, into the region of the spreading CdTe
vapor between subliming granular CdTe and the substrate to be
coated. A disadvantage here is found to be that the granular CdTe
is also oxidized in the vessel, which has an adverse effect on the
vapor yield.
[0009] A further known process for deposition of CdTe layers is
what is called "Vapor Transport Deposition", abbreviated to VTD. In
the VTD deposition method, CdTe is converted to the vaporous state
in a vessel and the CdTe vapor is guided by means of the gas stream
of an inert carrier gas into a coating zone in which the CdTe vapor
is deposited on a substrate. The VTD deposition method is usually
used for coating of the top side of a substrate with the coating
direction from the top downward. DE 10 2010 051 815 A1 discloses,
for example, a process for forming at least one photovoltaic
component in which an absorber layer which is produced from CdTe,
for example, can be deposited by means of VTD.
[0010] "Vapor transport deposition of large-area polycrystalline
CdTe for radiation image sensor application", Keedong Yang, Bokyung
Cha, Duchang Heo, and Sungchae Jeon, Phys. Status Solidi, C 11, No.
7-8, 2014, pages 1341-1344, describes the deposition of CdTe layers
by means of VTD for image sensor applications.
[0011] In the case of deposition of a CdTe layer by means of VTD,
it is possible to intercalate further chemical elements into the
CdTe layer, for example by adding a gaseous component of the
chemical element to be incorporated to the carrier gas. If oxygen,
for example, is added to the inert carrier gas, however, this has
an adverse effect in that the oxygen reacts with particles of the
CdTe vapor to give cadmium oxide during the transport of the CdTe
vapor to the coating zone, which reduces the quality of the layer
deposited.
[0012] The invention is therefore based on the technical problem of
providing a method of depositing a CdTe layer on a substrate, by
means of which the disadvantages from the prior art can be
overcome. More particularly, it is also to be possible by the
method of the invention to intercalate additional chemical elements
into the layer deposited without bringing about any chemical change
in the material being evaporated, for example through
oxidation.
[0013] In the method of the invention, a CdTe layer is deposited on
a substrate by means of physical gas phase deposition within a
vacuum chamber. Substrates used may, for example, be glass
substrates on which one or more layers of materials other than CdTe
may already have been deposited prior to the deposition of the CdTe
layer. Alternatively, it is also possible to use substrates of
metal or of plastic. In the method of the invention, a substrate to
be coated with CdTe, prior to the deposition process, is heated to
a coating temperature and then moved past at least one vessel in
which CdTe is converted to a vaporous state, in such a way that the
CdTe vapor formed is deposited on the surface of the substrate to
be coated. It is a feature of the method of the invention that at
least one further chemical element which can affect the electrical
conductivity of the CdTe layer, for example, is intercalated into
the CdTe layer deposited. This is achieved in accordance with the
invention in that a gaseous component having an elevated pressure
(relative to the vacuum in the vacuum chamber) flows through at
least one inlet against the surface of the substrate to be coated,
such that the gaseous component is adsorbed on the surface of the
substrate to be coated before the substrate is guided past the at
least one vessel in which CdTe is converted to a vaporous state.
The gaseous component adhering on the substrate surface is then
also incorporated into the layer that forms in the subsequent vapor
deposition of the CdTe.
[0014] The method of the invention can be executed, for example,
using a gaseous component comprising at least one of the elements
from the group of oxygen, nitrogen, sulfur, chlorine, fluorine,
phosphorus, arsenic, antimony, bismuth, tellurium. Oxygen as a
gaseous component is particularly suitable when the CdTe layer is
deposited as a constituent of a solar cell layer system because the
intercalated oxygen enhances the desired diffusion of chlorine and
sulfur into the CdTe layer from adjoining layers, which brings
about an elevated efficiency in the solar cell.
[0015] In one embodiment of the invention, the substrate is
repeatedly moved past the at least one vessel in which CdTe is
converted to a gaseous state, with adsorption of a gaseous
component at the surface of the substrate to be coated before each
entrance of the substrate into the coating zone of the vessel.
These may be the same gaseous components every time or else
different gaseous components from time to time. Alternatively, it
is also possible for multiple vessels in which CdTe is converted to
a vaporous state to be arranged in succession in a vacuum chamber,
viewed in direction of movement of a substrate, with adsorption of
a gaseous component on the surface of the substrate to be coated
each time before a substrate enters the coating zone of a vessel,
in that the gaseous component flows through at least one inlet
against the surface of the substrate to be coated.
[0016] In a further embodiment, the gaseous component is activated
by means of a plasma before and/or after the adsorbing on the
substrate surface, which can improve the incorporation of chemical
elements of the gaseous component into the CdTe layer.
[0017] Preferably, a CdTe layer is deposited in the method of the
invention by means of a CSS process. Alternatively, a CdTe layer
can also be deposited in accordance with the invention by means of
VTD.
[0018] It is also possible in the method of the invention for the
CdTe vapor to be activated by means of a plasma, which can
influence the properties of the CdTe layer deposited.
[0019] The present invention is elucidated in detail hereinafter by
a working example. FIG. 1 shows a schematic diagram of a device by
means of which the method of the invention is performable.
Substrates 2, on one side of which a CdTe layer is to be deposited
as part of a solar cell layer system, are guided through a vacuum
chamber 1. The chemical element oxygen is also to be intercalated
very uniformly into the deposited CdTe layer.
[0020] In the working example, the substrates consist of glass, on
which a TCO layer and subsequently a CdS layer have already been
deposited in preceding processes. Before the substrates 2 are
guided into the vacuum chamber 1, these have been heated to a
coating temperature. The heating of the substrates 2 to a coating
temperature or the maintaining of a coating temperature of the
substrates 2 can alternatively also be effected within the vacuum
chamber 1, for example by means of radiative heaters.
[0021] Within the vacuum chamber 1, there are three vessels 3
arranged in direction of substrate movement, which is illustrated
by an arrow above the substrates 2. Within the vessels 3 there is
granular CdTe 4, which sublimes owing to supply of heat to the
vessels 3. The substrates 2 are guided over the vessels 3 at a
distance of just a few millimeters, as a result of which a CdTe
layer is deposited on the substrates 2.
[0022] According to the invention, viewed in direction of substrate
movement, there is a gas inlet 5 disposed upstream of each vessel
3, out of which oxygen flows in the direction of the substrate
surface to be coated. The flow direction of the oxygen in the
working example is at right angles to the substrate surface to be
coated. The oxygen is adsorbed on the substrate surface to be
coated, is guided adhering to and together with the substrate 2
into the coating zone of a downstream vessel 3 and incorporated
into the layer deposited in the layer deposition there.
[0023] If a substrate 2, as described in the working example, is
guided repeatedly through the coating zone of one or more vessels 3
and a gaseous component is adsorbed beforehand on the substrate
surface to be coated each time, the method of the invention
provides a means of incorporating at least one additional chemical
element uniformly across the layer thickness profile of a CdTe
layer.
[0024] Because the substrates 2 are guided over the vessels 3 at a
distance of just a few millimeters, firstly, the lateral
evaporation losses are very small and, secondly, only very little
oxygen gets to the granular CdTe owing to the small gap between
substrate 2 and the vessel edge in connection with the relatively
high vapor pressure that builds up within the vessel 3 in the
region between granular CdTe 4 and the substrate 2. As a result,
the degree of oxidation of the granular CdTe within the vessels 3
is negligibly small and the vapor yield is very high.
[0025] It is known that, in the case of a solar cell layer system,
the deposition of a CdTe layer is followed by activation of the
CdTe layer with a chlorine compound in such a way that chlorine is
to diffuse into the CdTe layer. It has been found that,
surprisingly, the inventive intercalation of oxygen into a CdTe
layer promotes both the inward diffusion of chlorine owing to
subsequent chlorine activation and the inward diffusion of sulfur
from a CdS layer deposited beneath the CdTe layer. In the case of
solar cells having a CdTe layer deposited in accordance with the
invention, it was therefore possible to ascertain higher efficacy
compared to methods without oxygen intercalated in accordance with
the invention.
[0026] An analysis of CdTe layers deposited in accordance with the
invention has also shown that the inventive intercalation of oxygen
into a CdTe layer does not lead to formation of cadmium oxide
within the CdTe layer.
[0027] It should be noted once again that the method of the
invention is capable not just of incorporating oxygen into a CdTe
layer but also other chemical elements that have already been named
above, in order for example to dope the CdTe layer. The three
vessels 3 shown in FIG. 1 are also merely illustrative in terms of
their number. Depending on an objective, the method of the
invention can also be conducted with more or fewer than three
vessels 3 and the corresponding gas inlets 5.
* * * * *